
What makes the join is the second to last line: "AND x.intronum=y.intronum", which joins the tables together.
// Look for and list intros for each mount point.
$query2 = "SELECT x.sequence as sequence, x.intronum as intronum, y.filename as filename ";
$query2 .= " FROM ".$xoopsDB->prefix("uhqiceauth_intromap")." x";
$query2 .= " LEFT JOIN ".$xoopsDB->prefix("uhqiceauth_intros")." y ON x.intronum=y.intronum";
$query2 .= " WHERE x.server='".$row['server']."'";
$query2 .= " AND x.port='".$row['port']."'";
$query2 .= " AND x.mount='".$row['mount']."'";
$query2 .= " ORDER BY sequence";